Effects of varying energy and roughage in rations for lactating dairy cows on feed intake and milk production. Effects of varying energy and roughage in rations for lactating cows on rumen volatile fatty acids and milk composition

Hoogendoorn, A.L.; Grieve, C.M.

Journal of Dairy Science 53: 1034-1041


ISSN/ISBN: 0022-0302
Accession: 014455750

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(b) Molar concentrations of total volatile fatty acids in rumen liquid were greater and pH was lower early in lactation than in late lactation. Energy in the ration did not affect the molar proportions of acetate, propionate, butyrate or valerate, but the proportion of isobutyrate decreased and isovalerate increased with increased energy. Increase of roughage was associated with a significant increase in the molar proportion of acetate and a decrease in the proportion of propionate. Percentage milk fat was significantly higher when cows were given more roughage; percentages of milk protein and solids-not-fat were significantly greater when cows were given more energy. More energy was also associated with significant increases in the C8: 0, C10: 0, C12: 0 and C14: 0 fatty acids and C18: 0, C18: 1 and C18: 3 acids decreased significantly. In general, there was a greater incorporation of long-chain fatty acids into milk fat during the first half of lactation, associated with loss of bodyweight. Increase of roughage significantly increased the C4: 0, C6: 0 and C18: 3 fatty acids and significantly decreased the C18: 2 acid.